Preparations for tinting and coloring hair are an important type of cosmetic agent. They can be used for more or less pronounced shading of the natural hair color depending on the individual's desires, for achieving a completely different hair color, or for covering unwanted color tones, such as shades of gray, for example. Depending on the desired color or permanence of the coloration, common hair dyes are based either on oxidation dyes or on direct dyes. Combinations of oxidation dyes and direct dyes are also frequently used in order to achieve special nuances.
Coloring agents that are based on oxidation dyes result in brilliant and permanent color tones. However, they require the use of strong oxidizing agents such as hydrogen peroxide solutions, for example. Such coloring agents include oxidation dye precursors—so-called developer components and coupler components. The developer components form the actual dyes under the influence of oxidizing agents or atmospheric oxygen among one another or under coupling with one or more coupler components.
Coloring agents that are based on direct dyes are often used for temporary coloration. The direct dyes are dye molecules that are applied directly to the hair without the need for any oxidative processes to produce the color.
Some important representatives of this class of dyes are triphenylmethane dyes, azo dyes, anthraquinone dyes or nitrobenzene dyes, each of which can carry cationic or anionic groups.
With all of these coloration processes, the situation can arise in which, for any of various reasons, the coloration needs to be undone completely or partially. The partial removal of the coloration is expedient, for example, if the coloring result on the fibers turns out to be darker than desired. On the other hand, the complete removal of the coloration can be desired in some cases. For instance, it may be desired to color or tint the hair with a certain nuance for a specific occasion and to restore the original color after several days.
Means and methods for color removal are already known from the literature. One method for reversing coloration that is sufficiently known from the prior art is the oxidative decolorization of colored hair, for example with the aid of a common bleaching agent. In that process, however, the fibers can be damaged as a result of the use of strong oxidizing agents. Furthermore, reductive processes for color removal have also already been described. For example, European patent application EP 1300136 A2 discloses a hair treatment method in which the hair is colored in a first step and decolorized again reductively in a second step. Here, the reductive decolorization is performed using a formulation including a dithionite salt and a surfactant. In WO 2008/055756 A2, the reductive decolorization of keratin fibers is performed using a mixture of a reducing agent and an absorbing agent.
When using reductive decolorizing agents, the decolorization occurs through the reduction of the dyes located on the keratin fibers or hair. As a result of the reduction, the dyes are generally converted to their reduced leuko form. During this process, the double bonds present in the dyes are reduced, thereby interrupting the chromophoric system of the dyes and converting the dyes into a colorless form.
One general problem with the reductive decolorizing agents known from the prior art is that, while the colored keratin fibers can be decolorized using the reducing agent, the color removal is not permanent. Particularly in the case of oxidatively colored hair in which the coloration is produced on the hair through oxidation dye precursors of the developer and coupler type, colorations having very good fastness characteristics are obtained in part. When using the reductive decolorizing agent, these dyes are now converted reductively into uncolorized compounds—which, however, due to their similarly good fastness characteristics, remain on the hair.
After rinsing-off of the reducing agent, and under the effect of atmospheric oxygen, these reduced forms can be gradually reoxidized. This reoxidation results in a more or less pronounced recoloring. This recoloring generally does not match the color tone in which the keratin fibers were previously colored, but rather can be unattractive and is therefore all the less desirable for the user of the decolorizing agent.
It was therefore the object of the present invention to provide a decolorizing agent for decolorizing colored keratinic fibers that decolorizes colored keratinic fibers in a maximally complete manner. This decolorization should be long-lasting, and the decolorized keratin fibers should not experience any recoloration, nuance shift, or darkening under the effect of atmospheric oxygen. The decolorizing agent should exhibit good decolorization performance particularly on keratin fibers that were previously colored using oxidative colorants based on developer- and coupler-type oxidation dye precursors.
Surprisingly, it was found that the redarkening occurring after application of the reductive decolorizing agent can be effectively suppressed if the reductively decolorized keratin fibers are treated again with a post-treatment agent after decolorization that includes one or more acids from the group of the inorganic and/or organic acids and one or more zwitterionic and/or amphoteric surfactants.
Furthermore, other desirable features and characteristics of the present invention will become apparent from the subsequent detailed description of the invention and the appended claims, taken in conjunction with this background of the invention.